Automatic lubrication systems are used on many types of machinery, from large fixed plant to smaller mobile construction and mining equipment. In general they replace procedures requiring manual application using grease guns and the like.
Throughout this specification the lubricant is referred to as grease, being the most common lubrication substance, but the term is to be understood to include other lubricants such as oil and synthetic liquids or gels.
Known automatic centralised lubrication systems provide a useful function, but have some problems. It is not necessarily obvious to the machine operator when the automatic lubrication system is not delivering grease to all the bearings, due to some malfunction of the lubrication system. For example a broken connecting line can simply allow the full grease charge to be wasted, with none going to the injectors, or a malfunctioning injector can starve one bearing of lubricant. More sophisticated systems have alarms and sensors to provide oversight of operation, often in combination with an electronic sentry system, but such equipment is often not compatible with mining, earth moving and construction equipment as being too unreliable in the harsh environment in which these machines operate.
Malfunction of the lubrication system can be caused by air entrained in the grease in a reservoir. All greases are viscous, by definition, and release air reluctantly. Many greases are formulated as a stiff gel that effectively does not release air at all. Air may be entrained in the grease in many ways including:
When the system reservoir is recharged:
There may be air in the hoses connecting to the filling system;
Air may be pumped in when the drum of grease becomes emptied:
The suction spear may not protrude far enough into the grease in the drum so that a mixture of air is drawn in:
There may be an air leak in the suction of the filling system:
Or the grease may have air entrained in the drum as delivered.
With more fluid greases, an air bleed can assist in removing air from the reservoir. Some pump systems use a reservoir without a follower piston and a motor driven paddle to assist in mobilising the grease to the pump inlet that will also assist in air release with some greases, but this does not always effectively bleed the air.
The effectiveness of the lubrication system can be severely reduced by air. The grease in the pump becomes compressible so that less grease is delivered, or in some cases none at all. The delivery line effectively becomes a hydraulic accumulator as the air in the line becomes compressed and presents a potential safety hazard. Grease that is delivered to the bearings may be aerated, reducing the lubrication effectiveness.
Once air is distributed through the lubrication system often the only recourse is to shut the machine down and purge the reservoir, the pump, all the feed lines and the injectors of air. This generally requires that all the individual feed lines to the bearings be disconnected to allow the grease/air mixture to be discharged. Altogether this is a long and costly process having significant impact on machine productivity.
The invention aims to provide a method of automatically purging air from the grease pump delivery before it is distributed through the system, and preferably to also provide a single robust central monitoring point to indicate that the grease pumping system is operating correctly.